Prior art "3-lite" lamps of the type, for example, shown in FIG. 16, of Swasey et al. U.S. Pat. No. 3,156,843 are provided with two filaments which are mechanically and electrically connected to a special three "Kon-Tact" base in such a manner that, in combination with suitable switching means, light of three different intensities and corresponding wattages can be selected. For example, a 50-200-250 watt lamp of this type is one which is provided with a 50-watt filament and a 200-watt filament.
These lamps are generally operated in a "base down" burning position, for example, in a table or floor stand fixture to provide a low light level (50-watt), a medium level (200-watt) or a high light level (250-watt) for reading. "Base down" means that in operation, the lamp bulb and filament are located above the bulb base and socket.
Such lamps have evolved into shorter overall length lamps than comparable standard lamps of similar wattage. For instance, the now standard 200-watt A23 lamp has a maximum overall length, as recommended by the American National Standards Institute specification number ANSI C78.100-1976 of 6-5/16 " while a comparable 5/2/250/A23 "3-lite" lamp has a maximum overall length of 5-5/16". The resulting difference of 1" is also reflected in the filament location within the lamp, commonly referred to as LCL or "light center length". LCL is the distance from the center of light source to the base center contact. In order to center the filament at the maximum bulb diameter, the LCL of the 200-watt A23 lamp is 45/8" and that of the three-light lamp is 35/8".
The resultant compactness of the lamp structure in "3-lite" lamps of this type has created problems when such lamps are desired for use in a "base up" orientation. One problem involves the glass arbor button to which the filament support wires for such lamps are affixed. The glass arbor button is located below and adjacent to the filaments. In the "base down" orientation of the lamp, the hot gases emanating from the filaments deposits gaseous material on the lamp envelope and does not damage the glass button support. However, in the "base up" orientation such gaseous material deposits on the glass arbor button support assembly increasing heat absorption and eventually causing the button to melt. Even when melting does not occur, copious amounts of H.sub.2 O are evolved from the glass, thus shortening lamp life. The resultant short life when burning lamps in the "base up" orientation has restricted the design and development of new fixtures and has thus significantly limited the applications and market for such lamps.